This project addresses broad Challenge Area (03) Biomarker Discovery and Validation and specific challenge topic 03-DK-104: "Development of drug toxicity biomarkers for kidney, liver, and other organs of NIDDK interest for use in assessing human drug toxicity". Liver injury due to drug toxicity is a serious safety risk associated with drug development and poses a significant burden to physicians, the pharmaceutical industry, and regulatory agencies. Often, drug-induced liver injury (DILI) manifests as a rare, "idiosyncratic" event that occurs only in the rare, susceptible patient. This project will evaluate the use of a newly developed mouse model population, called the Collaborative Cross, to detect genetic variants that cause individuals to be susceptible to DILI. Once validated, this research tool will provide a unique means for evaluating the toxicity risk associated with pharmaceutical agents in susceptible patients as well as a means for which otherwise efficacious pharmaceutical agents may remain in public use, enabled by genetic testing. ABSTRACT Drug-induced liver injury (DILI) is the major adverse drug event that leads to regulatory actions on drugs, including failure to approve, restricted indications, and withdrawal from the marketplace. The most problematic form of DILI is "idiosyncratic", meaning the drug is safe for the vast majority of treated patients while causing catastrophic liver injury in the rare, susceptible patient. Genetic predisposition for complex traits, such as DILI, results from the combined effects of genetic variations within genes termed "quantitative trait loci" (QTL). Due to the rarity of these events, studies aimed at detection of causal risk alleles in human populations are often under-powered, thus hampering the ability to detect QTL. However, there are no animal models that have been validated for the ability to detect those genetic variants that confer an increased risk for liver toxicity for a given pharmaceutical. The project proposes a new paradigm for preclinical drug safety that is performed using a newly available mouse population, the Collaborative Cross, which was created specifically to model the genetically heterogeneous human population. The Collaborative Cross was developed using a breeding scheme that maximizes the genetic diversity between strains, allowing capture of 90% of the known genetic variation in mice. In three specific aims, our goal is to utilize the Collaborative Cross mouse population to identify genetic variants that predispose individuals for DILI. In Aim 1 - Determine the optimal drug and dose necessary to achieve a DILI response within the parental mouse strains of the Collaborative Cross - a dose- escalation study will be performed with ten drugs known to cause idiosyncratic hepatotoxicity. Phenotyping of liver injury markers will be performed to determine the optimal drug and dose needed for QTL analysis. Using the optimal drug and dose, Aim 2 - Determine genetic loci that modulate susceptibility to idiosyncratic DILI using the Collaborative Cross mouse strains - will be performed in 150 Collaborative Cross lines. These studies will utilize liver injury markers collected across the Collaborative Cross mouse population to interrogate genetic variations within the genome (i.e. single nucleotide polymorphisms;SNPs). The outcome of Aim 2 will be regions of the genome that are significantly associated with liver injury risk across mouse strains. To follow up on these studies, Aim 3 - Identify risk alleles for toxicity susceptibility within candidate gene regions - will be performed. Specific genetic variants that confer an increased risk of DILI, alone or in combination, will be identified by sequencing of target genes followed by correlation and risk ratio analysis of identified SNPs. These studies offer a unique opportunity to study the genetic architecture of predisposition to idiosyncratic DILI and have the potential to revolutionize how preclinical drug safety testing is performed. Successful completion of the proposed studies will provide a roadmap for improved drug safety testing, leading to safer drugs and a route to rescue efficacious drugs that cause toxicity in only a subset of the patient population PUBLIC HEALTH RELEVANCE: This project addresses a major challenge in the drug development process that greatly limits the utility and safety of drugs. Currently, most drugs are removed from the marketplace or are not approved for clinical use because of liver toxicity. No current platform exists to perform accurate preclinical testing of new drugs to identify those most likely to result in adverse events or to identify genetic factors that contribute to toxicity susceptibility. We are proposing a revolutionary new model based upon a mouse resource that was specifically developed to model the heterogeneous human population. The successful use of this new resource will dramatically improve drug develop, saving significant costs and greatly expanding the pharmaceutical industry.